An efficient and modified Quick Easy Cheap Effective Rugged and Safe (QuEChERS) method combined with liquid chromatography-electrospray ionization with tandem mass spectrometric detection were evaluated for the analysis of residues of 72 pesticides in brown rice including acidic sulfonylurea herbicides. For extraction of pesticides and clean-up of the extract, 1% formic acid in acetonitrile and dispersive solid phase extraction were used, respectively. Two fortified spikes at 50 and 200 µg L -1 levels were performed for recovery test. Mean recoveries of majority of pesticides at two spike levels ranged from 90 to 110% with standard error (Coefficient of Variation) less than 10%. The limits of detection and quantification ranged from 0.24 to 19.92 µg L -1 and 0.79 to 65.74 µg L -1 , respectively. Good linearity of calibration curves were achieved with R 2 > 0.9943 within the observed concentration range (from 20 to 400 µg L -1 ). The modified method also provided satisfactory results for sulfonylurea herbicides, which could not be determined properly with previously reported methods. This method was applied to determine residues of target pesticides in real samples. A total of 22 pesticides in 31 out of 40 tested samples were observed. The highest concentration was observed for tricyclazole at 1.17 mg L -1 . This pesticide found in two brown rice samples exceeded its MRL regulated for rice in Republic of Korea. Except this pesticide, concentrations of all observed pesticides were lower than their MRLs. The results reveal that the method is applicable for routine analysis of residues of target pesticides in brown rice.

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QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) method has been a lot of research for pesticide analysis, because it is very simple and fast. However, this method requires high sensitivity instrument such as LC-MS/MS because of the use of small sample volume and many impurities compared to the conventional method. So, QuEChERS method needs to be modified for using with HPLC and GC-ECD/ NPD. The aim of this work was to study the application of the QuEChERS method as well as its modification for the extraction and preconcentration of 5 groups of 61 pesticides from 4 fruits prior to their determination by HPLC-PDA, GC-ECD/NPD, and LC-MS/MS. The method was validated using spiking levels at 0.1 mg/kg (or 0.01 mg/kg) in apple, grapes, pear and persimmon. The average recovery by QuEChERS AOAC Official 2007. 01 version using the LC-MS/MS varied from 71.1127.4% for 61 pesticides. The average recovery rates using modified QuEChERS varied from 70.9~126% for 61 pesticides by HPLC-PDA and GC-ECD/NPD. The results satisfied the criteria of multiple pesticide residue analysis, setting 70~130% for recovery rates and below 30% for CV.

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